This invention relates generally to processes for making semiconductor integrated circuits.
In the so called damascene approach, copper layers may be formed in trenches within inter-level dielectric material. In some cases, the copper material ultimately forms metal lines for signal conduction. However, copper material may tend to diffuse causing adverse effects on nearby components.
Thus, it is desirable to provide a diffusion barrier to prevent the diffusion of copper atoms. Currently, tantalum or titanium based diffusion barriers are used. However, tantalum and titanium form native oxides which hinder direct electroplating of the copper onto the tantalum or titanium surface with acceptable adhesion and within-wafer uniformity.
Thus, it may be necessary to form a copper seed deposition in situ (in the same chamber used to deposit the tantalum or titanium based diffusion barrier). However, the need to provide a physical vapor deposition copper seed layer is cumbersome. Moreover, the adhesion between the overlying barrier material and the underlying dielectric may be unacceptable in some cases.
Thus, there is a need for better ways to provide diffusion barriers under copper layers.